1. Field of the Invention
The invention concerns a method for operating a powertrain, which comprises at least a drive unit and an automatic transmission.
2. Description of the Related Art
Automatic transmissions which are designed as range change transmissions and which have a multi-stage main gearbox and a range change group connected upstream or downstream of the main gearbox, as well as a splitter group connected upstream or downstream of the main gearbox have been known for many years and are preferably used in commercial vehicles. For example, by means of a two-stage splitter group which has a gear ratio step that corresponds to approximately half of a medium transmission stage between two sequential transmission stages of the main gearbox, the gear ratio steps of the main gearbox are divided in half which doubles the total number of available gears of the range change transmission. For example, by means of a two-stage range change group which has a gear ratio step that lies approximately by a medium gear ratio step between two sequential transmission stages across the entire gear ratio step of the main gearbox, the spread of the range change transmission is approximately doubled and the total number of available gears is again doubled.
Also known are automatic transmissions that have only one main gearbox. The splitter group and the range change group are therefore optional subassemblies of an automatic transmission, whereas it is possible to connect a range change group and/or a splitter group upstream or downstream of the main gearbox. Automatic transmissions comprising interlocking shift elements are different from automatic powershift transmissions comprising friction-locked shift elements.
Furthermore, it is known that such a powertrain of a motor vehicle with an automatic transmission can comprise an auxiliary output, whereas an auxiliary output can also be described as a power take off (PTO). In the context of auxiliary outputs a difference is made, on the one hand, between gearbox-sided and motor-sided auxiliary outputs and, on the other hand, between stationary and transient auxiliary outputs.
A motor-sided auxiliary output branches off a moment directly from the drive unit, whereas a gearbox-sided auxiliary output branches off a moment from the transmission. Stationary auxiliary outputs can be operated only when the motor vehicle is stationary, that is, when the automatic transmission is in neutral position, or when the power flow or torque flow from the drive unit to the axle drive is interrupted. Transient auxiliary outputs, on the other hand, can also be operated when a gear is engaged, that is, when the power flow or torque flow from the drive unit to the axle drive is not interrupted.
To date, it is possible only in a stationary motor vehicle to engage and thus activate a transient, gearbox-sided auxiliary output of such a powertrain of a motor vehicle having an automatic transmission. Furthermore, up to now, shifting is prevented when a gearbox-sided, transient auxiliary output is engaged or activated. As a result, driving is possible only in a single gear and, consequently, only in a limited speed range. Since, according to prior art, a gearbox-sided, transient auxiliary output can be engaged or activated only when the motor vehicle is stationary, the gear used must be a relatively low gear, namely a starting gear, because it has to be possible to start from a standstill.
The present invention concerns a method for operating a powertrain with an automatic transmission and a gearbox-sided, transient auxiliary output, in which it is possible to shift and, consequently, change gears when the gearbox-sided, transient auxiliary output is engaged and thus activated.
DE 10 2005 048 893 A1 has already disclosed a method for operating a powertrain with an automatic transmission and an auxiliary output, in which it is possible to perform a gearshift, or change of gears, when the auxiliary output is connected and thus engaged. In doing so it is imperative to synchronize by means of the drive unit via the clutch an input shaft of the automatic transmission.